Plastic refractory



Patented Aug. v 1947 PLASTIC REFRACTORY Herbert H. Greger and John J.Reimer, Washington, D. 0.; said Reimer assignor to The Briggs FiltrationCompany, Bethesda, Md, a corporation of Maryland No Drawing. ApplicationMay 2, 1946,

Serial No. 666,841 J 30 Claims.

This invention relates to high temperature plastic refractories and moreparticularly has reference to such plastic refractories capable of airsetting at room temperatures and above to produce bodies having highstrength.

This application is a continuation-in-part of our copending applicationsSerial Nos. 510,401 filed November 15, 1943, and 513,726 filed December10, 1943.

A plastic refractory consists essentially of a refractory filler such asceramic grog, a bond clay and some water to produce suflicientplasticity to permit molding by ramming, hammering, rolling or othersimilar meth'ods. Upon drying, the ceramic filler is bonded by the clayin the mixture. At temperatures below actual vitrification of the mass,the clay bond is naturally rather weak and therefore the material hascertain severe limitations which considerably reduce its usefulness.

In order to prevent the formation of a mass having low strength attemperatures below red heat, certain additional binders, such as organicand inorganic bonding substances, may be added to the plastic refractoryto effect a cementing of the clay and grog into a somewhat solidifiedbody. In some instances, sodium silicate has been added to achieve sucha cementing action. It is well known, however, that alkali metalsilicates are excellent fluxes and that they form with clay or othersilicates relatively low fusing glasses when subjected to the action ofheat. When such fluxing in the formation of low fusing glasses 2 theseincrease the strength of the dry specimens but the strength drops at 300to 400 C. (572 to 752 R), which is undesirable. If a refractory mortaris desired, the material must also have good adhesion to the brick,sufiicient plasticity for easy troweling, and a pyrometric coneequivalent similar to the brick.

Plastic refractories are mostly utilized in the formation of linings andfor patching the walls of various types of kilns and furnaces. Suchrefractories therefore are exposed to the highest heat in the kiln andmust possess good refractory properties. Obviously, the addition of anysubstances, such as sodium silicate, which would form a flux reducingthe melting points of the composition would detrimentally affect thedetakes place, the load bearing properties of the refractory mass areseverely reduced and in addition the refractory properties of thematerial are also reduced, the pyrometric cone equivalent being lowered.

An ideal plastic refractory is one which has high strength when dried inair and which maintains this strength until a ceramic body is developedabove 900 C.(1652 F). Most plastic refractories now on the market havelow strength when dried at room temperature and maintain this lowstrength until fired above 900 C. When sodium silicate is used, itincreases the strength at low temperatures but decreases therefractoriness of the body. When organic binders are used sirableproperties of the composition and would, in effect, defeat the purposefor which it was used.

The principal object of the present invention is I the production of aplastic refractory which avoids the disadvantages of the prior art.

Another object of this invention is to provide a plastic refractorycapable of air setting at room temperatures and above to form a materialhaving a high strength and which will maintain said high strength attemperatures up to those reached in firing.

A further object of this invention is to produce a plastic refractoryincluding a refractory filler, a high temperature bonding material andan aluminum phosphate binder for imparting a high strength bond to thematerial upon air setting at low temperatures.

Still another object of this invention is to provide plasticrefractories having desired plasticity, minimum shrinkage during dryingand during firing and having high strength before and after firing and ahigh degree of serviceability.

Another object of this invention is to provide a refractory mortarcapable of air setting at room temperatures and above to form a materialhaving high strength and which will maintain said high strength andfurther improve it at temperatures reached by firing to red heat andabove.

It is also an object of this invention to provide an air settingrefractory mortar containing an aluminum phosphate binder having goodproperties for trowelling or making of dip joints, a minimum ofshrinkage during drying and during firing, high strength before andafter firing, and a high degree of serviceability.

With these and other objects in view, the present invention resides inthe provision of a plastic refractory material comprising a filler suchas ceramic grog and/or other refractory particles, a clay binder and analuminum phosphate binder.

In accordance with the present invention, a plastic refractory or mortaris made by mixing together a composition comprising ceramic grog and/orother refractory material, a clay binder and an aluminum phosphate.Water is added to.

the mixture to produce a composition having the V desired plasticity andthen the substance is ready for use. After the material is appliedormolded; it is air dried and due to the addition of the alu-' minumphosphate a high strength is imparted to the air dried or set material.This strength is maintained and gradually increased when the product isheated from 100 C. up to and above vitrification temperatures.

The plastic composition according to the present invention as beforeindicated comprises a refractory material such as ceramic grog and otherrefractory substances, a binder'such as clay and an aluminum phosphate.It has been found that plastic refractories having the followingcompositions exhibit the desired properties in accordance with thepresent invention:

1. Plastic refractory P23K Parts -4+20 mesh fire clay grog 45.00 -35+48mesh calcined kyanite 2.51 48+100 mesh calcined kyam'te 2.73 100 meshcalcined kyanite 19.10 Kentucky ball clay #4 7.61 Georgia kaolin 7.82Sesqui aluminum phosphate 5.23 Water 10.00

2. Plastic refractory P33K Parts 4+20 mesh fire clay grog 45.0 35+48mesh calcined kyanite 2.8 48+100 mesh calcined kyanite 3.0 100meshcalcined kyanite 20.0 Kentucky ball clay #4 8.0 Georgia kaolin; 8.2Sesqui aluminum phosphate 3.0 Water 10 0 3. Plastic refractory P35KParts -4+20 mesh fire clay grog 45.0 35+48 mesh calcined kyanite 2.848+100 mesh calcined kyanite 3.0 -100 mesh calcined kyanite 13.5Kentucky ball clay 14.0 Georgia kaolin 8.2 Sesqui aluminum phosphate 3.0Water 1 10.5

" ble type.

4 4. Plastic refractory composition (P. C. E.

Gone 34) Parts 3+4 mesh grog (cone 35) 12.0 -4+20 mesh grog (cone 35)34.7 20+35 mesh grog (cone 35) 9.0 -35+48 calcined kyanite (cone 36) 2.748+100 calcined kyanite (cone 36) 4.5 calcined kyanite (cone 36) 4.7Kentucky ball clay #4 (cone 32) 8.3 Taco clay (cone 35) (pure kaolin)12.5 Mono-aluminum phosphate 2.6 Water 10.0

1 Aluminum phosphates added to the compositions for effecting a bondupon air setting at low temperatures are hydrated aluminum phosphates ofan essentially colloidal but water solu- The compositions near thesesqui-aluminum phosphate or between 1 and 1% mols of alumina and'6 molsof phosphoric acid may be considered the preferred range for purposes ofthis invention.

Depending on water content and composition or the ratio of alumina tophosphate radical, the properties of these phosphates undergo aconsiderable change. The mono-aluminum phosphate is a solid only inessentially water-free state, while the sesqui-aluminum phosphate maycontain as much as 25 per cent, the dialuminum phosphate may contain asmuch as over 30 per cent water 0f hydration and still be a solid. Moredetails as to the properties of these phosphates will be found in PatentNo. 2,405,884 issued August 13, 1946, to Herbert H. Gregor.

In suitable concentration, they form tacky viscous solutions of goodadhesive quality, which increasessomewhatfrom the monoto thesesqui-aluminurn phosphate. Plastics containing the sesqui-alurninumphosphate exhibit usually better strength, and workability, than thosecontaining the mono-phosphate. The lower phosphates, including themonoand the sesqui-phosphate, have-been successfully used in plastics.They are somewhat hygroscopic with a decrease of the hygroscopicproperty from'the monoto the sesqui-aluminum phosphate. The compositionsof higher aluminum content than the sesqui-phosphate have the tendencyof giving off water from their solutions rather than absorbing it fromthe air. These can be produced in the form of a stable water solubleglass containing about 25 to 30 per cent of water of hydration.

This hydrated, solid type of aluminum phosphate can be used to advantagealso in preparing a dry plastic refractory mixture. This type ofphosphate is essentially inert to the atmosphere. It can be pulverizedto a fine powder and disperses readily in water.

Such a plastic refractory is prepared essentially from volume stablerefractory grog or other filler of low porosity. Depending on the use orthe pyrometric cone equivalent value of the grog, its particle size.etc., the porosity of the filler particles themselves may vary betweenpractically zero to 17 or 18 per cent. The preferred porosity, however,is low or not exceeding about 5 per cent.

In order to reduce shrinkage and limit the exposed rain surface of thefiller, its particle size may be as coarse as minus 2 /2 or 3 mesh (toas fine as minus 20 mesh). These large particles reduce the need for alarge quantity of bond and plasticizing water, and usually between 15 to25.

per cent of high grade refractory clay and about 2 /2 to, 5 per cent andup to 10 per cent and even.

higher of aluminum phosphate on a. dry basis is satisfactory forobtainingthe desired strength. It has been found that even smallerpercentages of aluminum phosphate will improve the green strength of theplastic refractory, the ranges mentioned giving'the optimum results witheconomy of materials. Also higher concentrations of the aluminumphosphate give desirable results. The amount of water may vary butaverages about parts per 100 of the above dry mixture. Clays containinga fair percentage of montmerillonite, magnesia, lime and alkali metalsshould not be used as these will react and precipitate the phosphate. Apure kaolin is the most suitable clay in conjunction with aluminumphosphate solutions as it is stable and highly refractory. Wheresomewhat impure kaolins must be used they can be greatly improved forpurposes of this invention by a mild acid wash, as for instance, dilutesulfuric acid.

The refractory properties of a plastic refrac tory and also of arefractory mortar are largely controlled by the type of filler, and thepyrometric cone equivalent value of the filter. For instance, a goodkaolin has a pyrometric cone equivalent value of 34 or 35 which is truealso of the grog prepared from it. Such materials as kyanite, mullite,diaspore, certain flint clays, Alundum, chromite, silicon carbide,andalusite, calcined topaz, have pyrometric cone equivalent values of 36and above. Some of these materials may be used in either calcined or inraw form. At the inversion temperature between 1400 to 1550 C., i. e.during formation of mullite and glass from kyanite, andalusite,sillimam'te, certain flint clays and also from topaz, an expansion involume takes place which is relatively moderate in andalusite and maytherefore make it possible of even using this material partly or whollyin raw uncalcined form as filler in a plastic refractory, This volumeexpansion can be utilized for counteracting shrinkage in the refractoryand wholly eliminate it.

This shrinkage of a well compounded plastic is usually less than 2%. Itmay also be of interest to note that the plastic of Example 4 has apyrometric cone equivalent value of cone 34 and a spalling loss of only0.5% in standard spalling tests which permit a range up to 5%.

In the common non-air setting plastic, 3, condition of low resistance tothe disintegration by water exists unless it is fired to a minimumtemperature of 500 C. The air setting plastic containing aluminumphosphate becomes resistant to slaking in boiling water on drying at 100C. This property of resistance to slaking is of considerable importancein many installations and uses of the composition.

The aluminum phosphates covering the whole range of compositions fromthe mono-aluminum phosphate to the di-aluminum phosphate are to a largeextent interchangeable. They can be used interchangeably if an allowanceis made for the increase in viscosity from the monoto the dialuminumphosphate for the identical water content. It should also be noted thathydrolysis on dilution with water begins at lower water contents as thealumina content in the binder increases. If for any reason thehydrolysis limits must be extended, such compounds as aluminum chloride,sulphate or nitrate may be added. Also ammonium chloride, sulphate ornitrate may be used for the purpose, If concentrations as high as 1 molof aluminum chloride per mol of aluminum phosphate are used, then therange of composition may be extended even to the trialuminum phosphate.

In minor proportion, when added to a solid aluminum phosphate, thesesalts will increase the rate of dispersion of the solid powderedphosphate in water. For instance, the incorporation of aluminum sulphatein quantities of 10% (on dry basis) in the aluminum phosphate bindergave somewhat higher rates of solubility.. It was also found ofadvantage in some cases to incorporate organic matter, such asphosphoric acid solutions of proteins, carbohydrates, polyethyleneamines and related compounds, These solutions may be incorporated duringor after the formation of the binder.

Either the plastic refractory or the refractory mortar may be producedin a wet plastic form or as a dry powder. The wet form has already beendescribed. The dry powder does not differ fundamentally-from the wetplastic except in itsv water content, otherwise the formula remainsessentially the same and as shown for instance in: Example 4. The wateris added before use and. mechanical orhand mixing continued for some:time.

Of necessity, the mode of production of a dry plastic will differsomewhat from that of the wet material. The filler, clay and binder maybe mixed together in a loose, dry form. This method gives perfectlysatisfactory results in some instances but it was found that the binderin presence of the clay and the limited amount of water in the plasticwill not wet and bond the coarse grog particles quickly and completelyenough to form a Well coherent mass. While this condition is not seriousif a suitable mechanical mixer is available, some difficulty may beencountered when the composition is improperly mixed by hand.

The action of wetting is very considerably improved by coating the grogfirst with the aluminum phosphate binder. In addition to this advantage,it has been found possible to dry certain binder solutions on the grogand to incorporate it in this manner into the dry plastic refractory.

This procedure is applied principally to hinder compositions which aremost readily prepared in the form of solutions, i. e. those rangingbetween the monoand the sesqui-aluminum phosphate. This range may beextended to the di-aluminum phosphate by the addition of aluminumchloride, sulphate or nitrate.

The procedure is as follows: The binder is mixed in a mechanical mixerwith the total grog in the desired proportion of mesh sizes andquantities. The mixture is then dried in a conventional drier at ZOO-300F. The drying time for the thin film of binder on the grog is very shortand the procedure eliminates the need of specialized equipment fordrying the viscous and tacky binder, such as a flaking machine or spraydrier, of the grog is accomplished.

A further advantage in pre-coating the grog with the binder consists inclosing the pores of the grog which will normally be filled with water.This amount of water for saturating the grog will, therefore, beavailable in the initial stages of mixing for producing a reducedviscosity and for aiding in the mixing. After the binder is dissolvedfrom the pores, water will enter the grog.

It has been found that an improved product can be made by incorporatinga wetting agent At the same time, the necessary coating by adding about25% of a wetting agent: (such.

as a sodium alkyl naphthalene, sulphonateformulation) the green andvitrified; strength; of the product is improved. 7

Comparative tests have been made on the products of-the presentinvention with available commercial; refractories and the results were afol lows:

Modulus of rupture m pounds per square mch Sample No. Tgrzp Sample No. 1is the product of Example 1 without any aluminum phosphate.

Sample No. 2 is the product of Example 1.

Sample No. 3 is the product of Example 2.

Sample No. 4 is the product of Example 2, to which has been added .25%of the wetting agent.

Sample No. 5 is the product of Example 3.

Samples 6, 8, and 9 5 are commercial plastic refractory materials.

Sample '7 contains an organic bond.

SamplelO is a cast refractory.

For purposes of the above comparison, bars 4 /2 x 2 x 2" were made in ametal mold by subjecting the specimens to a thousand pounds per squareinch pressure in a hydraulic press. The test pieces were allowed to dryat room temperature for 24 hours and then transferred to an electricdryingoven operated at 110 C. where they remained for 24 hours, Aftercooling to room temperature, one set of specimens was tested for dry orgreen strength on an Olsen testing machine to determin the modulus ofrupture.

Sets of specimens were then fire to 200, 300, 400, 500, 600, 700, 800,900, 1000, 1100, 1200, 1300, and 1500 C. Specimens were fired up to 1000C. in an electric kiln and held at their respective temperatures for 5hours. The others were fired in a gas fired kiln, and held at theirrespective. temperatures for 5 hours.

In view of th foregoing results, it will be readily appreciated that theplastic refractories made in accordance with the present inventionexhibit both high green and fired strengths, While some of the prior artmaterials have high fired strengths, they lack high green strengths. Onthe other hand, those compositions which have a fairly high greenstrength lack a, high fired strength.

The plastic refractory is a ramming mixture and can be used not only forpatching and as a lining, but also for preparing special shapes, kilncrowns, kiln doors, tunnel kiln car tops, and possibly whole kiln wallscould be rammed or pressed. Small refractory articles such as crucibles,saggers, small furnaces, may be prepared by pressing and drying. Afterdrying the strength of these articles or shapes is sufiicient to standhandling or shipping. When installed and heated, a fire bond isdeveloped wherever the temperatureishigh and wher .thisisnot thecase thecoldset of the refractory issufficient'to resist th usual Wear-on thekiln. Some further improvement in the dry strength and vitreous strengthmay be, obtained if necessary by increasing the density of the wetrefractory by vacuum mixing, pug milling. or vacuum extrusion.

Akiln wall may be rammed against a wooden backing which is laterremoved. The rammin tools are 50 applied that their pressure or blowsare. not directed against the wooden backing, but almost verticallydownward with a slight deviation towards the wood. In thismanner onelayer can be placed on top of the other. The plastic refractory willsustain a considerable amount of Weight and the wall may be built up toa;con-

siderable height without collapsing. When the walls arecompletea-slowdrying fire maybe placed into the kiln and after the walls havehardened the crown may be placed on top. This may have been preparedeither in sections by ramming into a. suitable form or it may also-berammed in place. Various combinations of this rammingtechniquewith thecustomary construction-ofbrickare, of course, possible, and suchcombinations are in many cases the preferred method of construction.This is especially true.

of the combination of the rammed material with a structural insulatingbrick which then takes the outside or intermediate position in thefurnace wall. On the outside an insulating coating may be applied.

It has-been found that refractory mortars having the, followingcompositions exhibit the desired properties in accordance with thepresent invention:

Parts -35+48 mesh calcined kyanite (cone 35-36) 6.5 48+ mesh calcinedkyanite 26.0 l00 mesh calcined kyanite 19.4 Kaolin (Taco clay) (cone 35)13.3 Kentucky Ball clay No. 4. (cone 32) 8.9 Water 18.5 Mono-aluminumphosphate binder 7.4.

P. C. E. val ue,34..

Parts 35+48 mesh calcinedv kyanite- (cone 48+100mesh calcinedkyanite26.0

P. C. E. value 34.

Such a refractory mortar is prepared from essentially volume stablerefractory grog or other suitable filler of low porosity, In order toreduce shrinkage the particle size of the filler is kept as large aspossible; however it must be small enough to permit good workability introwelling and in making dip joints the mortar slurry must not showrapid segregation. These conditions limit the grain size of the grogusually to smaller than 35 mesh. Besides the finer mesh sizes of grog, ahigh grade refractory clay or a mixture of such clays is incorporated inthe mortar in amounts ranging between 15 to 40 per cent. To this mixtureof clay and refractory filler is added to 15 per cent or even more ofaluminum phosphate on a dry basis for obtaining the desired air settingproperty and strength. It has been found that even smaller percentagesof aluminum phosphate will improve the green strength of the refractorymortar, the ranges mentioned giving the optimum results with economy ofmaterials. Also higher concentrations of the aluminum phosphates givedesirable results. The amount of water may vary but averages about 25parts per 100 of the dry mixture.

The dry mortar after plasticization with water to trowelling or dippingconsistency as shown before in various examples, is useful for joiningfire brick. The dry mortar may also be used as a ramming mixture ifmixed with an amount of water considerably reduced and limited toapproximately to per cent. It can be used in this form for patching orfor the production of special shapes, small furnaces and crucibles byramming and pressing. After drying the strength of these articles orshapes is sufiicient to stand handling or shipping. When installed andheated, a fire bond is developed wherever the temperature is high andwhere this is not the case the cold set of the refractory mortar issufficient to produce an effective bond.

We have found that the adhesion of the mortar to the brick when used forbonding bricks together is improved if a wetting agent is incorporatedin the mortar. For this purpose, a wetting agent such as (a sodium alkylnaphthalene sulphonate formulation) is very suitable. A wetting agentmay be incorporated in either the wet mortar or in a dry mortar mix. Inthe latter instance, the wetting agent should be added in solid form tothe dry mixture. Such a wetting agent when incorporated in a dry mortarmix will dissolve when water is added to the mixture to produce a wetpaste.

A number of tests have been made on mortars prepared in accordance withthe present invention and it is believed that duplication of the resultswhich we have obtained employing standard test methods can beaccomplished by those skilled in the art. In evaluating test results thecomponent picture should be considered rather than individual resultsespecially in the case of air set strength of the mortars in comparisonwith the strength of fired mortars.

The pyrometric cone equivalent test indicated that air setting mortarshaving aluminum phosphate binders incorporated therein impart highrefractory properties to the mortars. In the case of the air settingmortars having compositions as set forth in Examples 1, 2 and 3, it hasbeen found that such compositions have a pyrometric cone equivalentequal to standard cone 34 (3200 F.) As indicated in the examples, thepyrometric cone equivalents of the components of the mixtures rangebetween cone 32 and cone 36.

iii

The results of a heat soak test at 2912 F. confirm the refractoryproperties indicated by the P. C. E. values. This test consists oflaying a pier of three bricks with the mortar, The top and bottom brickswere 9-inch straight brick while the middle section consisted of twohalfbricks. The pier of bricks was assembled in this manner in order tohave both vertical and horizontal joints. After drying at roomtemperature for 24 hours and at 220 F. for a further 24 hours, the pierof bricks was then mounted in a kiln and subjected to a temperature of2912 F. and held at that temperature for 5 hours. After the furnace wascooled, the pier of bricks was thoroughly examined and no evidence ofmelting or flowing of the joint material or any change in jointthickness could be found.

Another important test concerned the deformation at high temperatures.The mortars containing the aluminum phosphate binders are more resistantto deformation under load when subjected to elevated temperatures thanare mortars containing the customary silicate of soda binders. It wasfound that the mortar joint suspending the weight of a 9-inch standardfire brick over a span of 15 inches did not fail until a temperature of1490 C. was reached in comparison to 1420 C. for a mortarcontaining asodium silicate binder. The sodium silicate mortar apparently becamesoft at the failing temperature while the phosphate mortar was morerefractory and failure occurred between brick and mortar rather than inthe mortar itself. In places the brick surface was broken off andadhered to the mortar.

The mortars containing the phosphate binders show good bonding strengthswhen air dried as well as when fired to all temperatures before a firedceramic bond is developed in the mortar. The advantage of the aluminumphosphate lies in the fact that good strengths are developed at lowertemperatures and that the aluminum phosphate binder does not decreasethe refractoriness of the mortar at high temperatures. The followingtable gives an illustration of the bonding strengths that are developedat various temperatures by the air setting refractory'mortar containingsesqui-aluminum phosphate.

We have found that a very effective mortar of the dry type can beproduced by drying the liquid binder on the rog or kyanite. Twenty percent of the liquid binder was used, containing 50 per cent solidphosphate; it was mixed with the kyanite in the mesh sizes given inExample 3 in a mechanical mixer. The tacky mixture was fluffy and driedwell in an oven at 250 F. within 1 /2 to 2 hours. Occasional stirringnaturally promotes the drying.

In commercial practice, the mixture of kyanite and binder may be driedon a wire screen belt in a tunnel drier and since the material is quitefluffy warm air may be blown through it and thus the drying time couldbe considerably reduced. I

After breaking the loose aggregate up to a particle size of through 20mesh, it was mixed with the necessary amount of clay. This mixture isthe dry binder ready for packaging. For use it is mixed with water. If apower mixer is available about 15 minutes of mixing time were foundsufiicient to dissolve the phosphate. The less effective hand mixingmethods with a hoe take somewhat longer. If maximum strength is wanted,an aging period of 12 to 24 hours is recommended.

Air setting mortars containing solid silicate of soda require aconsiderably longer mixing time of from 2 to 5 hours, and developmaximum strength on aging for 12 to 24 hours.

A number of test bars were made from mortars of various compositions forpurposes of comparing their moduli of rupture. The test bars were firstdried for 18 hours at 70 C., then for 24 hours at 110 C. Some were thenfired to 815 C. The results of these tests are given in the followingtable:

No. or

Modulus Binder Rupture Batch N0.

A binders are prepared from pure alumina and B" binders ar prepared frombauxite and contain some clay, and minor quantities of titania and ironoxide as impurities.

Bodies D'TK and DSK contain solid powdered aluminum phosphate which wasnot dried on the kyanite but added as a loose powder.

Certain clays such as kaolinite and halloysite, but not montmerillonite(bentonite), have the ability of absorbing considerable quantities ofthe phosphate (P04) ion. Kaolinite will absorb about 37 g. andhalloysite about 41 g. of phosphate ion per 100 g. of the dry clay.These figures are almost exactly equivalent to the amount of thehydroxyl ion in the clay. The exchange of the hydroxyl ion for thephosphate ion is particularly effective with aluminum phosphatesolutions of low pH values, such as for instance at pH 0.5-2.5. The timeinvolved for completion of the reaction may extend over several weeksand depends to some extent on the particle size of the clay. Thephosphatization reaction produces an amorphous structure in the clay,which seems to be a contributing factor in the production of air settingmortar bodies of high strength. It also may explain in part why thestrength of some mortar bodies is improved on ageing.

The absorption of the P04 ion by the clay has naturally an importantrelationship to the compounding of refractory mortars of the wet type.There the quantity of the phosphate ion must be sufficient to satisfythe clay, and some must be left over in the aluminum phosphate bond tokeep this in a water soluble form. Usually mortars of the wet typecontain a large enough quantity of aluminum phosphate to meet theseconditions; however, it is necessary to choose a fairly acidic type ofphosphate (between the monoand the sesqui-aluminum phosphate), becausein the removal of part of the phosphate radical by the clay the aluminumphosphate will attain a higher aluminum content and in this manner evenbecome a solid. It is, therefore, necessary to guard against theformation of solid phosphate by adjusting both the quantity and thecomposition of the aluminum phosphate. In extreme cases where even themono-aluminum phosphate does not produce the desired results, additionalphosphate radical may be introduced by using aluminum phosphates of amore acidic nature than the mono-aluminum phosphate.

In mortars which are prepared in a dry form and where the interaction ofaluminum phosphate with clay is eliminated due to the dry form of thephosphate, a very interesting advantage is obtained by the promotion ofthe air set through the clay. When water is added to the dry mortar, theclay will begin to take up some of the phosphate radical and a shift inthe composition of the aluminum phosphate binder will occur and, in linewith the above explanation, the alumina to phosphate ratio willincrease. As the alumina content of these binders increase, they losethe hygroscopic properties and become hydrated solids, thus improvingthe rate and the quality of the air set.

From the foregoing, it will be appreciated that the present inventionprovides a mortar having good refractory properties and strength whenair set and when fired.

In the usual commercial dry air setting mortars, a powdered silicate ofsoda is used as binder which on exposure to air during storage isdestroyed by the carbon dioxide in the air. The aluminum phosphate isnot chemically attacked by carbon dioxide and deterioration of thebinder from this source will not take place.

While We have specifically described our invention with reference tospecific compositions and uses of the composition, it should beunderstood that the invention is not to be restricted to the specificdetails thereof but should be limited only by the appended claims.

We claim:

1. An air setting plastic refractory having high green and firedstrengths comprising about 15 to 25% of high grade refractory clay, arefractory filler, and about at least 2 /2 to 5% of water solublecolloidal aluminum phosphate ranging from monoto di-aluminum phosphate.

2. An air setting plastic refractory having high green and firedstrengths comprising pure kaolin, a refractory filler, and water solublecolloidal aluminum phosphate binder ranging from monoto di-aluminumphosphate.

3. An air setting plastic refractory havin high green and firedstrengths comprisin a refractory filler, a clay binder, and watersoluble colloidal mono-aluminum phosphate.

4. An air setting plastic refractory having high green and firedstrengths comprising a refractory filler, a clay binder, and watersoluble colloidal sesqui-aluminum phosphate.

5. An air setting plastic refractory having high green and firedstrengths comprising a. refractory filler, a clay bind-er, and about atleast 2 to 5% water soluble colloidal sesqui-aluminum phosphate.

6. An air setting plastic refractory havin high green and firedstrengths comprising a refractory filler, a clay binder, and watersoluble colloidal aluminum phosphate of a composition lying betweenthose of monoand di-aluminum phosphates.

7. An air setting plastic refractory having high green and firedstrengths comprising fire clay grog, calcined kyanite, ball clay,kaolin, and water soluble colloidal aluminum phosphate ranging frommonoto di-aluminum phosphate.

8. An air setting plastic refractory having high green and firedstrengths comprising fire clay grog, calcined kyanite, ball clay,kaolin, and at least about 2.5 to 5% water soluble colloidal aluminumphosphate ranging from monoto di-aluminum phosphate.

9. An air setting plastic refractory having high green and firedstrengths comprising a refractory clay, a refractory filler, watersoluble colloidal aluminum phosphate ranging from monoto dialuminumphosphate, and a wetting agent.

10. An air setting plastic refractory having high green and firedstrength's comprising fire clay grog, calcined kyanite, ball clay,kaolin, water soluble colloidal aluminum phosphate, ranging from monotodi-aluminum phosphate, and a wetting agent.

11. A method of reducing the spalling loss in plastic refractoriescomprising incorporating Water soluble colloidal aluminum phosphateranging from monoto di-aluminum phosphate in the composition thereof.

12. An air setting plastic refractory having high green and firedstrengths and a spalling loss of about .5% comprising a refractory clay,a refractory filler, and water soluble colloidal aluminum phosphateranging from monoto dialuminum phosphate.

13. An air setting refractory mortar having high air set and firedstrengths comprising kaolin, a refractory filler or smaller thanthirty-five mesh particle size, and a water soluble colloidal aluminumphosphate ranging from monoto dialuminum phosphate.

14. An air setting refractory mortar having high air set and firedstrengths comprising a refractory filler of smaller than thirty-fivemesh particle size, a clay binder, and water soluble colloidalmono-aluminum phosphate.

15. An air setting refractory mortar having high air set and firedstrengths comprising a refractory filler of smaller than thirty-fivemesh particl size, a clay binder, and water soluble colloidalsesqui-aluminum phosphate.

16. An air setting refractory mortar having high air set and firedstrengths comprising a refractory filler of smaller than thirty-fivemesh particle size, a clay binder, and water soluble colloidal aluminumphosphate of a composition lying 1.4 between those of monoanddi-aluminum phosphates.

17. An air setting refractory mortar having high air set and firedstrengths comprising fire clay grog of smaller than thirty-five meshparticle size, calcined kyanite, ball clay, kaolin, and water solublecolloidal aluminum phosphate lying between monoand di-aluminumphosphate.

18. An air setting refractory mortar having high air set and firedstrengths comprising a refractory clay, a refractory filler of smallerthan thirty-five mesh particle size, a water soluble colloidal aluminumphosphate ranging between monoand di-aluminum phosphate, and a wettingagent.

19. An air setting refractory mortar having high air set and firedstrengths comprising fire clay grog of smaller than thirty-five meshparticle size, calcined kyanite, ball clay, a water soluble colloidalaluminum phosphate ranging between monoand di-aluminum phosphate, and awetting agent.

20. An air setting refractory mortar having high air set and. firedstrengths comprising a refractory clay, a refractory filler of smallerthan thirty-five mesh particle size, and 5-15% of a water solublecolloidal aluminum phosphate ranging between monoand di-aluminumphosphate.

21. An air setting refractory mortar having high air set and firedstrengths comprising a refractory filler of smaller than thirty-fivemesh particle size, a clay binder, and 515% of a water soluble colloidalsesqui-aluminum phosphate.

22. An air setting refractory mortar having high air set and firedstrengths comprising fire clay grog of smaller than thirty-five meshparticle size, calcined kyanite of smaller than thirtyfive mesh particlesize, ball clay, kaolin, and 5- of a water soluble colloidal aluminumphosphate ranging between monoand di-aluminum phosphate.

23. An air setting plastic refractory having high green and firedstrengths comprising a refractory filler, a clay binder, and a watersoluble colloidal aluminum phosphate of a composition ranging betweenthose of monoand di-aluminum phosphates having admixed therewith analuminum salt of a strong inorganic acid.

24. An air setting plastic refractory having high green and firedstrengths comprising a refractory filler, a clay binder, and a watersoluble colloidal aluminum phosphate of a composition ranging betweenthose of monoand di-aluminum phosphates having admixed therewith anammonium salt of a strong inorganic acid.

25. An air setting plastic refractory having high green and firedstrengths comprising fire clay grog, calcined kyanite, ball clay,kaolin, and water soluble colloidal aluminum phosphate ranging frommonoto di-aluminum phosphate having admixed therewith an aluminum saltof a strong inorganic acid.

26. An air setting plastic refractory having high green and firedstrengths comprising fire clay grog, calcined kyanite, ball clay,kaolin, and water soluble colloidal aluminum phosphate ranging frommonoto di-aluminum phosphate having admixed therewith an ammonium saltof a strong inorganic acid.

27. An air setting refractory mortar having high air set; and firedstrengths comprising a refractory filler of smaller than thirty-fivemesh particle size, a clay binder, and water soluble colloidal aluminumphosphate of a composition lying between those of monoand di-aluminum15. phosphates having admixed therewith an aluminum salt of a stronginorganic acid.

28. An air setting refractory mortar having high air set and firedstrengths comprising a refractory filler of smaller than thirty-fivemesh particle size, a clay binder, and water soluble colloidal aluminumphosphate of a composition lying between those of monoand di-aluminumphosphates having admixed therewith an ammonium salt of a stronginorganic acid.

29. An air setting refractory mortar having high air set and firedstrengths comprising fire clay grog of smaller than thirty-five meshparticle size, calcined kyanite, ball clay, kaolin, and

